The Appendix Quarter Horse
Until the 1940s the American Quarter Horse existed as a type rather than a breed, but in 1940 a group of breeders discussed the idea of forming an association. However, there was disagreement about what constituted a Quarter Horse. Many types existed and some horses had a lot of Thoroughbred blood, while others did not. One solution was to grade the horse types as A, B, C or D. Although never implemented, the Appendix Quarter Horse registry rose from this idea. The C type horse is now an Appendix. This describes a horse with a Thoroughbred sire or dam bred to a Quarter Horse dam or sire.
The influx of Thoroughbred blood helped the Quarter Horse evolve from the heavily muscled, shorter bulldog horse of the 1930s and 40s. The Thoroughbred added size, refinement and withers, which is important for saddle fitting. The Appendix Quarter Horse continues to mix the unique aspects of the Thoroughbred with the Quarter Horse.